Rotating components in a gas turbine engine can, in rare situations, become released from their mounts. Containment systems are provided in a gas turbine engine to capture these released components and dissipate a significant proportion of the energy of the component.
The fan cases in particular, owing to the length of the fan blades, is one of the largest components on the engine—the fan case of the Trent XWB has a diameter of around 3 meters. Because of its size the fan case is often one of the heaviest components of the engine.
Fan cases have, in the past, had a rigid outer skin within which a low density liner is positioned and which can crush during impact of a released blade to absorb some of the energy. The outer skin is typically of a similar or higher hardness than that of the released blade which prevents the blade passing through the casing.
Unfortunately, the use of materials similar to that of the blades is expensive due to the price of the material. Other materials which offer the same or greater hardness are typically much heavier and the significant use of these would increase the weight of the engine to an unacceptable level.
Material with less weight is typically softer than the material of the blade. The use of this material for the containment case increases the risk of blade fragments passing through the casing to an unacceptable level.
One solution that has been proposed in the related art is that described in US2008/0199301 where the casing is of a two part construction with a containment ring of first material mounted with an interference fit within a casing of a lighter and softer material e.g. aluminium.
It is an object of the present invention to seek to provide an improved casing for a gas turbine.